Add llvm-c-test tool for testing llvm-c

This provides rudimentary testing of the llvm-c api.

The following commands are implemented:

  * --module-dump
    Read bytecode from stdin - print ir

  * --module-list-functions
    Read bytecode from stdin - list summary of functions

  * --module-list-globals
    Read bytecode from stdin - list summary of globals

  * --targets-list
    List available targets

  * --object-list-sections
    Read object file from stdin - list sections

  * --object-list-symbols
    Read object file from stdin - list symbols (like nm)

  * --disassemble
    Read lines of triple, hex ascii machine code from stdin - print disassembly

  * --calc
    Read lines of name, rpn from stdin - print generated module ir

Differential-Revision: http://llvm-reviews.chandlerc.com/D1776